Unfortunately not.

With the benefit of hindsight, Bronica should have made the SQ with both 6x4.5 and 6x6 backs and just one set of lenses and not bothered with the ETRS. Instead, they produced the 6x4.5 ETRS first followed by the SQ.

Lenses which fit the ETRS will also fit the ETRSi and the ETRC but not any of the SQ or GS series.